Field
The present disclosure relates to methods and associated systems for the suppression of metallic fires.
Description of Related Art
A liquid metal-cooled nuclear reactor, also referred to as a liquid metal fast reactor (LMFR), is a fast neutron nuclear reactor where the primary coolant is a liquid metal. Various types of liquid metals with relatively high heat capacities (which provide thermal inertia against overheating) may be used as the primary coolant. An example of a liquid metal-cooled nuclear reactor is a sodium-cooled fast reactor (SFR). In a sodium-cooled fast reactor (SFR), liquid sodium is used as the primary coolant instead of water. Water is difficult to use as a coolant for a fast reactor, because water acts as a neutron moderator that slows the fast neutrons into thermal neutrons. In contrast, sodium atoms are much heavier than both the oxygen and hydrogen atoms found in water. As a result, the neutrons lose less energy in collisions with sodium atoms. Sodium also need not be pressurized since its boiling point is much higher than the reactor's operating temperature. Furthermore, sodium does not corrode steel reactor parts.
A potential concern for a sodium-cooled fast reactor (SFR) is the leakage of sodium. Sodium is a pyrophoric metal and will ignite spontaneously when contacted with air and/or water. The exothermic reaction of sodium with air and water is shown below by the following equations.2Na(l)+O2(g)→Na2O2(s)4Na(l)+O2(g)→2Na2O(s)2Na(l)+2H2O→2NaOH(aq)+H2(g)Notably, sodium hydroxide (NaOH) is caustic and hydrogen (H2) is flammable. Additionally, sodium peroxide (Na2O2) and sodium oxide (Na2O) will also form sodium hydroxide (NaOH) if contacted with water.
Conventionally, a metallic fire (e.g., sodium fire) in a nuclear reactor is extinguished by inerting the area where the pyrophoric metal (e.g., sodium) is leaking. The inerting may be achieved with a vacuum pump that is used to remove the air from the area of the leak while supplying an inert gas (e.g., nitrogen, argon) which does not react with the pyrophoric metal. By removing the reaction source (e.g., oxygen) from the area of the leak, the metallic fire may be extinguished. However, this inerting approach is dangerous to plant workers who may be in the area of the leak and, thus, accidentally exposed to the oxygen-deficient environment.